1. Field of the Invention
This invention relates to thickeners for aqueous systems based upon polyethers of high molecular weight.
2. Prior Art
Polymeric water-soluble thickening agents are widely used for many purposes. Commercially available polymeric thickeners differ widely in chemical composition. The diversity of available thickening agents is an indication that not all are equally useful. It is not unusual to find some thickening agents which perform well in a certain environment and not at all in another environment. In fact, in some uses, no one thickening agent is completely satisfactory and there is a continual need and a continuing search for new thickening agents to satisfy many unmet needs. For instance, various cellulose derivatives or other water-soluble polymers such as sodium polyacrylates, polyacrylamides and polyethylene glycol fatty acid diesters are representative thickening agents. The polyethylene glycol fatty acid diesters are widely used for textile printing emulsions, cosmetic emulsions, and aqueous pigment suspensions. These esters suffer from the defect that they are not resistant to hydrolysis in an acid or alkaline medium so that under such conditions the thickening effect initially obtained is gradually reduced.
Polyoxyalkylene compounds, including high molecular weight materials are well known for use as surface-active agents, as disclosed in U.S. Pat. No. 2,674,619. These compositions can be prepared at high molecular weights, for instance, up to 25,000 for use as aqueous thickeners. It is known that liquid polyoxyalkylenes can be obtained by utilizing a mixture of ethylene oxide and another lower alkylene oxide in an oxide ratio of from 75 to 90 percent ethylene oxide to 10 to 25 percent other lower alkylene oxides such as propylene oxide, as taught in U.S. Pat. No. 2,425,755. The polyether polyols of the prior art having high thickening efficiency are generally those having the highest molecular weights reasonably obtainable under commercial conditions with price considerations being a limiting factor. Because high molecular weight polyethers require a disproportionately longer processing time to produce, it would be desirable to prepare high efficiency thickeners utilizing lower molecular weight polymers.
In U.S. Pat. No. 3,538,033, there are disclosed polyoxyalkylene derivatives of diepoxides having thickening properties. The thickener compositions disclosed are useful for thickening aqueous systems and are prepared by reacting a diepoxide compound having at least 12 carbon atoms with an alkylene oxide adduct containing from 100 to 250 moles of ethylene oxide units.
In U.S. Pat. No. 3,829,506, there are disclosed biodegradable surface-active agents having good foam properties and foam stabilizing characteristics prepared by copolymerizing ethylene oxide alone or with another lower alkylene oxide and an alpha olefin oxide in the presence of a polyhydric alcohol. Molecular weights of 400 to 6000 are claimed but there is no indication that the compositions are useful as thickening agents for aqueous systems.
In U.S. Pat. No. 3,475,499, there is disclosed the preparation of glycols and glycol ethers by reacting with water 1,2-epoxides having 3 to 30 carbon atoms. The compositions are disclosed as useful in the preparation of detergents. High molecular weight polyether block polymers are disclosed in U.S. Pat. No. 3,535,307. Such compositions have molecular weights of about 2000 to about 25,000 and are useful in the preparation of polyurethanes.